Hot Water Cylinders

What system is the best to ensure you have the hot water you need?

Hot Water Cylinders

There are two main types and a couple of sub-types of hot water cylinder:

The most common cylinder would be the copper immersion cylinder. Usually found within the airing cupboard and coupled to a cold water storage tank in the loft. This is what we know as a Gravity system.

It will give many years of trouble-free service and has been the mainstay of UK systems for generations. However, the shortfalls of this type are:

  • You need a large volume of stored water in the loft
  • The pressures necessary to efficiently run modern-day showers and taps is often too low. Most shower valves won’t work at all with a gravity-fed system.
  • They take up valuable space, usually in the middle of the house, where the space could be used for something more attractive.

This benefit over a combi boiler system is that you’ll have an electric immersion back-up should the boiler fail which will keep you with hot water.

Unvented cylinder

Another type and one that is fast becoming the most popular for larger homes, would be the Unvented cylinder.

The unvented cylinder will give you mains pressure hot water at the taps and showers, usually restricted to 3 bar which is plenty for any shower valve or tap type.

This benefits of this over the gravity system are:

  • No stored water in the loft space
  • Mains pressure from all taps and showers
  • Can be positioned at any level in the house and is often sited in a garage or utility room.

And the benefit over a combi boiler system is that you have an immersion back up should the boiler fail.

The drawbacks are:

  • It is a more expensive item to purchase and install
  • It requires more maintenance than a gravity system


Sub-types of unvented cylinder are

  • The under-sink heater – an all electric version of an unvented cylinder in miniature form. Used when there is a minimal requirement for hot water such as a utility sink where there is no hot water supply.
  • The oversink heater – often found in industrial office blocks and workshops simply heats the water on its way to the tap.  With a very slow flow rate, it has a place but only as a last resort.
hot water coming out of tap

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